Production of phenol by oxidation of benzene



Patented Mar. 27, 1951 UNITED STATES- PATENT OF PHENOL BY OXIDATION PRODUCTION OFBENZENE FFICE George Ghislain Joris, Convent, N. J.,*assign0r to Allied Chemical '& Dye Corporation, New York, N. Y., a corporation of New York I No Drawing. Application September21, 1948, Serial No.50, 12

invention relates to the oxidation of ben-.' zone to phenol by means of elementary oxygen lower the temperature requirement e. g. to about 7 400.? C. at 100 atmospheres pressure; but equipment for operation at increased pressure is expensive and there is danger in operating a. hydrocarbon oxidation process above atmospheric pressure because of the increased possibility of leaks from the equipment of poisonous, explosive vapors.

It has been proposed in order to lower the temperature required for air oxidation of benzene to phenol to employimpure benzene as their'eed in excess over the benzene which. will be oxidized in each reaction cycle and to withdraw excess puri-. fied benzene at the end of each cycle thus maintaining in the feed an appreciable concentration of impurities which serve to reduce the necessary operating temperature.

9 Claims. (01. 260- 621) convert benzene to phenol by action of elementary 1 oxygen, a reaction temperature within the range of about 250-400 C. is maintained in the reaction zone, and besides the benzene introduced in the reaction zone there is introduced into the "reaction zone from about 1- to about 20 volumes per 100 volumes of benzene of at least one ma} terial of the group consisting of open chain hydrocarbons. containing in the molecule at least one unbranched, saturated chain of at least 3 carbon atoms; cyclic saturated hydrocarbons containing at least 6 carbonatoms; and mixtures of normally liquid, non-aromatic hydrocarbons l which mixtures contain at least about percent by liquid Volume of one or more of the aforesaid aliphatic or cyclic hydrocarbons. may be admixed with benzene, and this mixture may supply part or all of the benzene for my a process.

atmospheres (absolute). Volume ratios given herein refer to volumes of the materials in the f vapor state.

The introduction of the above materialsin quantitiesvvithin the specified ranges with total However, the tempera? ture reduction obtained in accordance with this proposal is only moderate: this method allows e.-g. using a temperature of about 450 C. at.50 atmospheres pressure. a

One object of my invention is to promote vapor phase air oxidation of benzene to phenol. at pressures of the order of one atmosphere with output comparable to that of prior art processes at like pressures but at temperatures in the. vicinity of 330-350 C., which allows more accurate temperature control than in the prior art processes and reduces the severity of the conditions to which the oxidation equipment is subjected. Another object is to obtain improved yields of phenol on the aromatic hydrocarbon attacked as compared to the yields by prior art processes. another object is to obtain valuable co-products of oxidation along with the phenol. Other objects and advantages of my invention will appear hereinafter.

Still- In accordance with my improvement in'oxida- 1 tion processes which operate at a pressure of the order of one atmosphere in the vapor phase to pressures of the order of 1 atmosphere results, I

have found, in the appearance of a temperature range with lower limit about 250 C. and upper limit about 400 C. within which comparatively rapid oxidation of the aromatic hydrocarbon and the above foreign material occurs to form a phenol and products of incomplete oxidation of the foreign material plus some carbon oxides and a other products. Below about 250 C. the reaction rate is small. The temperature of most' 5 rapid reaction and greatest phenol output per pass within the temperature range employed in my process is usually about 330- 350 .0. Above about 330-350 C. the reaction rate drops, more or less sharply depending on what promoter is used,'on space velocity, as will be discussed below,

and on promoter concentration. At tempera-' tures above about 450 C. (i. e. above the temperature range of my process) the reaction'rate 1 once more rises with increasing temperature and at about 500 C. (in the presence of the pro' motors) oxidation of the reaction mixture again is rapid.

The promoter itself as well as the aromatic hydrocarbon is in part oxidized forming in addition to carbon oxides valuable compounds such as acetic acid and formaldehyde. These compounds the other products and can be separated from recovered.

The promoter By pressures of the order of 1 atmosphere I 'mean pressures between about 0.5" and about 5' Among the foreign materials suitable for incorporation as oxidation promoters in reaction mixtures according to my process are straight chain hydrocarbons such as normal pentane, normal hexane, normal heptane, normal octane, and normal decene-l; branched chain hydrocarbons: such as 2-methylpentane; cyclic hydrocarbons such as methyl-cyclopentane, and cyclohexane and its homologs either pure or in mixtures such as gasolines high in naphthenic. hydrocarbon. content; and hydrocarbon mixtures, for example straight run gasolines, cracked gasolines and kerosene fractions, which mixtures contain. sub-- stantial proportions of an open chain. or a cyclic hydrocarbon promoter admixed with nonaromatic hydrocarbons, such as lower branched chain aliphatic hydrocarbons, themselves not necessarily good promoters. Apparently, the good promoters activate the poor ones in a hydroca-rbon: mixture. such as va.straight-run gasoliner since. such gasolines areas satisfactory as pure straight chain or cyclic hydrocarbons as. pro-- moters. Preferred promoters; of the. above, group. are; those boiling withinthe, range from about 30 C. to, about 225 63., particularly about. 7 C. to. about 1-20? The quantity of; promoters present should be. sufficient to: bring about theoxidation of substantial. amounts, of benzene. in. one pass. of the reaction; mixture through the reaction zone. This requires a minimum; of. about. 1. volume. of promoter. per 100. volumesoi benzene in the reaction mixture. If the quantities. of promoter present are small. the. quantity of. phenolappearing in; the liquid products. of one pass depends. linearly on. the; volumes of promoter introduced. per L00 volumes of input benzene. For theoxidationof benzene to phenol with normal heptanev as; promoter, for example, this linear. relation extends. up. to about. 5. volumesof promoter per 95- volumes of benzene in the. input gases- The. curve continues. upwardr but less. than. linearly, above the 5:95 ratio. Preferred rati'os1,.. giving. satisfactory production of phenol. andiow productionof carbonoxides. are. betweenabout 5: I00 and about :10.0, An input volume ratio of promoterzbenzene of. about. 20:10.0 represents a suitable upper limit. for promoter. concentration. in. my process.

Allof the. promoters, show in commonthe property of forming with air at temperatures in. the range 2503-400 C; compounds containingv oxygen. which readily enter into oxidation reactions. These, compounds. apparently are, peroxides. The. promoters alsoshow. in common when. pure the phenomenon of cold; flames during. their re.- action. with air in the temperature range; 2.50-

400" C. That. is, thepromoter compounds when.

heated within this temperature range. with. suitable proportions. of, air produce in. the, reaction,

vessel,. without much. accompanyingrise in. temperature,v a luminous glowing region. Actual. ignition. o ccurs only on suffi'ciently raising, the temperature, increasing v the pressure, or otherwise. alteringv the reaction. conditions...

I. believe that. the. previously described lowtemperature oxidation. range from about 25.0 400 C. within which my process operates is-associated with peroxide, formation from. the ioreign promoter material; and. that. the. falling off. in. oxidation rate with. increasing temperaturesv observedbetween about.350.. Qand. about 450? C... is associated with. acceleration. of. processes. in. which decomposition of the peroxides is. faster than their reaction with benzene. The high temperature oxidation occurring from about 450 C. up appears due to a reaction distinct from that occurring in the temperature region below about 400 0., used in my process. However, I do not intend to limit the scope of my invention by'this or any theory of my; process;

With the less active promoters, use of pressures above atmospheric and up to 5 atmospheres may be desirable to promote formation of peroxides The following examples are to be understood asv illustrative of the invention but not as limiti'ng the scope of the invention.

Example 1.A metered flow of air saturated with benzene by bubbling the air through a containerof benzene. maintained at constant temperature was mixed with a metered flow of normal. heptane and passed down a heated Pyrex glass tube of 2" O. D. and 4 length at a space velocity of input, gases and vapors (STP), based on the total volume of the tube; of 1-00- reciprocal hours. The first foot of the tube functioned as" a preheater section. Temperatures were measured by a series of thermocouples down the tube. The temperature recorded below as' reaction temperatureisthetemperature maintained in the hottest zone of the reactor; Theexit gases were passed first through atrap at about C. to remove tars, then through two scrubbing towerspacked withstainless steel helices. The first tower was. kept at about 50-65 6. to condense through. charcoal. traps to: adsorb residual v mate rials such as benzene; the gases leaving thechar coali traps. were: sampled for analysis: regularly: during the run and. a. portiorr was continuously? collected for analysis; by displacement. of water: in a storage bottle; The charcoal. traps: were pe riodically' heated in a. stream of nitrogen and; the gas containing: desorbed: materials. was. passech to. thebenzene: evaporator;

The quantities of all. products collected were measured. The phenolic product. was analyzed for phenol. by bromination to tribromophenol'i The; aqueous. products. collected: in; the secondi tower: were analyzed for acid; and aldehyde. conztent; anch theorganic products collected' in. the. second. tower: and in the benzene saturator" an the: end of. the run. were analyzed: forbenzene and heptane: by sulfonation of components other'tharr. benzene and. heptane: and; measurement of re;- fractive index of: thex-unsultonated residue-..

Thev input. volume: ratio of ai'rzbenzene vapor. in the aboverun was about 1; the input-volume ratio of normal heptane benzeneyapdrswasiilflfiy the reaction temperature was 3&0 C1; and thedurationof therunwas 31 hours:

The benzeneattacked during the run per part by weight of phenol formed was about: 1:2'partsr representing about 2% of the total benzene cir culated' to thereaction zone during the" reaction period, The normal heptaneattacked' on the The yield of phenol based on the benzene attacked'represents 69% of theory and the'carb'on oxides "formed represent only 18% of theory based on the benzene and the heptane attacked. N-hexane, n-pentane, and Z-methyl. pentane when-substituted for'n-heptane in the procedure ofthis example likewise promoted the oxidation of benzene to phenol.

Example 2.A series of runs was made atvarying temperatures to test the efiect of cyclohexane as a promoter. The reaction tube was a heated vertical 40 mm. 0. D. Pyrex glass tube '70'cms. long. Metered flows of air, benzene and cyclohexane were introduced at the ,top of the tube. as a preheater. Temperatures recorded as reaction temperatures are'the temperatures main.- tained in the hottest zone of the reactor.

The product gases were passed through a Dry Ice trap to condensethe liquid products and the non-condensable gases were analyzed for oxygen,

carbon monoxide and. carbon dioxide. Phenol was determined in the liquid products by bromination to tribromophenol.

With a space velocity of input gases and vapors (STP) of Y150 reciprocal hours based on the total volume of the reaction tube, 1 volume ratio of air:hydrocarbons, and 1:19 volume ratio of cyclohexanezbenzene in the input gases and at a reaction temperature of 333 C., 19% of the input oxygen was consumed and 1.8% by weight of phenol was found in the liquid products. The

number of mols of carbon oxides formedby oxi 1 dationof the feed permol of benzene in the feed oxidized to phenol was 6.1 mols. At a reaction temperature of 309 C. under conditions otherwise'the same 9% of the input oxygen was consumed and 1.0% of phenol was found in the liquid products. The number of mols of carbon oxides formed per mol of benzene oxidized to phenol was 1.32. At 349 C. reaction temperature the percent oxygen consumption was 12% instead of 19% at 333 C. and the phenol found in the liquid products amounted to 1.4 weight percent instead of 1.8%. The number of mols of carbon oxides formed per mol of benzene oxidized to phenol was 4.44.

Similar results were obtained when instead of cyclohexane a gasoline containing large proportions of eyclohexane homologues was employed as promoter using the procedure of the above example. Methylcyclopentane employed similarly at temperatures about 340 C. and space velocities of about 100 per hour likewise promoted oxidation of benzene to phenol.

Example 3.The apparatus used in this example was like that of Example 1 except that the reactor was a 3 inch inside diameter, 4 foot long aluminum pipe; and an additional scrubbing tower in which exit gases contacted water countercurrently was placed after the ice-water cooled scrubbing tower.

the been an;

The upper part of the tube functioned A run of 13 hourswas carried out as in Exam: 7

ple 1 but with a straight-run, debutanized, sul-fifuric acid treated Pennsylvania gasoline of boil-' ing range 30 to 102 C. as promoter. This gasoline contained approximately 35% by liquid volume of straight-chain hydrocarbons, 31% by liq-w uid volume of branched-chain aliphatic hydrocarbons and 34% by liquid volume of cycloparaffins. The volume ratio of airzhydrocarbon va-. pors was 1:1; the amount of the gasoline promoter contained in the benzene circulated to the reaction zone was'about 5% by weight, and thetemperature in the hottest zone of the reactor. was about 330 'C. The oxygen content of the exit gases, initially about 15% by volume, fell? during about volume. The results obtained are' summarized in the. followingtable in which the numerical values '1 are per'part by weight of phenol produced,

Benzene circulated to reaction zone; 2 71 parts? Consumed (parts); i r

'7 hours to a value of about.10% by Analysis for phenol was as tribromophenol; for. total aldehydes was by the hydroxylamine methad; for formaldehyde was by the colorimetric method using basis fuchsin indicator; for totalf.

acids was by titration with alkali using phenolphthalein indicator; and for formic acid was by treatment wtih mercuric oxide followed by stand-v ardacid titration.

Variables in my process such as ratio of air: hydrocarbon and space velocity may be within the ranges previously known for processes in which aromatic hydrocarbons are oxidized to phenols. Particularly suitable values for these variables are noted below.

Particularly suitable input volume ratios of airzvapors of organic reactants in my process are from about 5:1-1:5. Preferably a ratio of about 1:1 is employed since this ratio allows a satisfactory level of phenol output accompanied by a low value for the mols of carbon oxides produced per mol of phenol formed.

Space velocities of input gases and vapors (STP), based on the total volume of the reactor, of about 20 per hour and up are suitable for my process. Space velocities of about -300 per hour are especially suitable since these space velocities are conveniently obtained and lead to satisfactory levels of phenol output. A space ve locity of about -150 per hour represents the preferred value in this range. The higher the space velocity, the greater is the output of phenol in unit time when the phenol outputs per pass are maintained. At high space velocities the peak for the curve of phenol output per pass vs. tem perature becomes increasingly sharp; according! am nes-1 The apparatus used tocarry out my process may be constructed in accordance with previously known construction of apparatus for exothermic vapor phase oxidation processes employing as oxidizing agent a gas, such as air, containing elementary oxygen. The construction materials may be chosen from those previously known for vapor phase air oxidation of aromatic hydrocarbons to phenols. Thus the reaction zone may be constructed of or lined with for example glass, boron oxide, or aluminum.

Preferably the apparatus provides for recycling unreacted benzene and promoter back to thereactioni zone. The recycled material may contain partial. oxidation products dissolved therein.

Preferably, provision is made for recovering otherproducts, e. g. products obtained from the promoter, as well as for recovering phenol. For example, a water extraction of the crude phenolic product followed by benzene extraction of the aqueous phenol solution may be used to separate phenol from other products and to recover these products. The benzene solution of phenol resulting may then be distilled to recover pure phenol therefrom without substantial loss due to formation of tarsduring the distillation process.

I claim; v

1. In the process for oxidizing benzene to phe- 1101 in vapor phase at pressures of the order of one atmosphere with elementary oxygen, the immovement which comprises introducing into the reaction zone benzene, oxygen and from 1 to volumes (as vapor, per 100 volumes of benzene vapor introduced into the reaction zone) of at least one material of the group consisting of open chain hydrocarbons containing. in the molecule at least one unbranched saturated chain of at least 3 carbon atoms; cyclic saturated hydrocarbons containing at least 6 carbon atoms; and mixtures of normally liquid, non-aromatic hydrocarbons which mixtures contain at least about by liquid volume of hydrocarbon promoter aforesaid; and maintaining reaction temperatures in the hottest zone of the reactor. in the range from 250 C. to 400 C.

2. A process in accordance with claim 1 in which the space velocityrof the input vapors (STP) is at least-about 20 volumes per hour per.

unit volume in the reactor.

3. A process. in accordance with claim l whichv the promoter material introduced with the benzene is a gasoline fraction. I v

,4. A process in accordance with claim li'n which phenol is separated from other products by a water extraction of the crude phenolic prod not followed by a benzene extraction of the resulting aqueous phenol solution 5. A process in accordance with claim I which the oxygen employed is oxygen of the-ail and the input volume ratio of airzorganic re actants in vapor state is within the range 5: 1 1:5.

6.- A process in accordance with claim 5 inwhich the reaction temperatures are withinthe range of about- 330-350 C., the space" velocities based on the total reactor volume, of the input gases and vapors under standard conditions are- .betw'eenabout '75 andabout 300 per hour, and

the ratios of input promoter vaporszinput berrzene vapor are between about 5:100 and 10: 1 00.

'7. A process in accordance with claim 6 where-- in the promoter material boils within the rangeof about C. to about 120 C.

8. A process in accordance with claim 6 i which the promoter material is a straight run.

gasoline fraction, the input volume ratio of air'zr hydrocarbons in vapor state is between about 1:1

and. about 1:3, and the space velocity of the gases and vapors is between about and about 159- per hour.

9. A process in accordance with claim 6- which the promoter material introduced with;

the benzene is a fraction containing a large proportion of cyclohexanes boilingwithin the range from about 70 to C.

GEORGE GHISLAIN JORIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Krieble et al. Apr. 20. 1948; 

1. IN THE PROCESS FOR OXIDIZING BENZENE TO PHENOL IN VAPOR PHASE AT PRESSURES OF THE ORDER OF ONE ATMOSPHERE WITH ELEMENTARY OXYGEN, THE IMPROVEMENT WHICH COMPRISES INTRODUCING INTO THE REACTION ZONE BENZENE, OXYGEN AND FROM 1 TO 20 VOLUMES (AS VAPOR, PER 100 VOLUMES OF BENZENE VAPOR INTRODUCED INTO THE REACTION ZONE) OF AT LEAST ONE MATERIAL OF THE GROUP CONSISTING OF OPEN CHAIN HYDROCARBONS CONTAINING IN THE MOLECULE AT LEAST ONE UNBRANCHED SATURATED CHAIN OF AT LEAST 3 CARBON ATOMS; CYCLIC SATURATED HYDROCARBONS CONTAINING AT LEAST 6 CARBON ATOMS; AND MIXTURES OF NORMALLY LIQUID, NON-AROMATIC HYDROCARBONS WHICH MIXTURES CONTAIN AT LEAST ABOUT 25% BY LIQUID VOLUME OF HYDROCARBON PROMOTER AFORESAID: AND MAINTAINING REACTION TEMPERATURES IN THE HOTTEST ZONE OF THE REACTION IN THE RANGE FROM 250* C. TO 400* C. 